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Looking for a primer thinner and don't know which one is needed for your paint? The marketplace offers undercoat thinners of any type. This section contains only specialized products developed by the best manufacturers of marine paints and varnishes.

If choosing a primer thinner is difficult for you, contact the experts of our marketplace for a free consultation. If you want to know more about preparative thinners and getting primers of the required consistency, you can get answers to all your questions by phone, via the website’s feedback form or email ([email protected]).

Surface priming is considered a mandatory technological operation that must be performed before any type of painting. The primer is applied both to above-deck structures, the hull sections above the waterline, and to the underwater parts of the hull made of wood, metal and fiberglass.

Obviously, with such a wide range of applications, primer compositions can also vary greatly. Therefore, there is no clear answer to the question of which thinner is best to dilute the primer. The answer will depend on the type of material used, as well as the properties of the surface being painted and the working conditions. In order to choose exactly the type of solvent that is optimal for a particular situation, we will describe the most common options.

How to Choose a Thinner

Before you start selecting a thinner for a primer, you should know why dilution of the primer may be necessary and in what proportion it should be done; it is important to know the goals that are pursued when priming.

The primer is applied to achieve one or more results:

strengthen the weak and crumbling surface of the base;
fill the pores to increase the mechanical strength of the material and eliminate the effects of absorption;
increase adhesion (adhesion to the surface) when applying the main coating layer;
reduce the consumption of more expensive finishing paint by reducing the number of layers required;
fill minor surface defects, making it smoother;
protect the metal base from corrosion, and the wooden base from mold and rot.

A well-applied primer layer significantly increases the service life of the coating and increases its decorative and protective properties.

Problems of Primer Dilution

First of all, it is necessary to understand the difference between the terms “solvent” and “thinner” in relation to substances used to dilute paint materials. Often these words are considered synonyms and the difference between these products isn’t noticed. Indeed, most often in most cases the solvent can act as a diluent (the reverse is not always true). But there are situations and types of work when the use of a solvent for dilution is not recommended, since it will negatively affect the final condition of the coating.

The thinner is used to reduce the viscosity of liquid primer and make it more fluid. This may be required when choosing the appropriate method for applying the material to the surface - working with a roller usually requires a more liquid material than using a brush. Pneumatic atomization will require an even greater degree of dilution, to a viscosity level comparable to ordinary water.

The solvent is more active and is capable of converting highly thickened and even dried particles of the binder into a liquid state. This requires the use of other chemicals whose molecules have a higher solvating ability. Therefore, it is possible that moments when paint or primer, which does not interact with the surface of the base, after adding a solvent, unexpectedly begin to show activity in relation to the substrate.

When is a Thinner Better Than a Solvent?

In practice, there are cases where, having used an active solvent without taking into account the possible effect on the base, it was necessary to redo the work, re-carrying out the preparatory stage. In the worst case, it was also necessary to completely replace the thinned paint with new one.

Such effects are also possible in situations related to ship repair work.

Painting interior finishing elements made of polyurethane foam with acrylic or even oil paint is permissible if you do not first try to dilute the thickened material with aromatic hydrocarbons (xylene) or a compound solvent containing them.
Repainting is done over the old paint without completely removing the entire layer. Excessive solvent activity will lead to dissolution of the base binder, after which bubbles may appear, surface peeling, and other undesirable effects.

In the described and a number of similar cases, the use of a mild primer thinner instead of the used active solvent would allow the work to be completed without unnecessary loss of time and budget expenses.

Types of Primers

Primers, similar to other types of paints and varnishes, are divided into types based on the type of film-forming material, each of which requires its own materials when diluting.

Alkyd primers. They are produced on the basis of oil varnishes, pentaphthalic or glyphthalic synthetic resins. For their dilution, a wide range of diluents and solvents based on aliphatic and aromatic hydrocarbons is allowed.

Highly active diluents with high penetrating ability for alkyds are xylene, butyl acetate, ethyl cellosolve. By using them, you can achieve excellent adhesion to metal or wooden surfaces. A less active diluent is white spirit, which is recommended as a universal substance for diluting alkyd materials.

Acrylic primers. They are divided into two large classes, which is why sometimes there is confusion following the advice of inexperienced authors. Compositions based on acrylic resins can be water-soluble and organic-soluble. They have completely different purposes and recommended solvents.

Water-soluble acrylic paints and primers, as the name suggests, are dissolved with ordinary water. They are widely used in construction for finishing interiors and facades, and penetrating acrylic primer is considered an indispensable step in any finishing of a plastered (putty) surface.

Attention! It is advisable to dilute even a water-soluble primer with water not from the tap, but after preparation: settling, filtering, boiling, etc. The reason is the low quality of water supplied by main water utilities, where the concentrations of hardness salts, iron and other impurities are often exceeded.

Organosoluble acrylic primers. This is a high-tech class of materials, most often used in multi-layer coatings of automobile bodies or yacht gelcoats. To work with it, each major manufacturer tries to release their own brands of thinners, which are marked with a common brand with other products in the series. The compatibility of the thinner and subsequent layers of paint and varnish materials is very important when choosing a product to achieve the required consistency of any primer.

It makes no sense to use a product labeled “acrylic primer solvent” for water-dispersion paint, and attempting a reverse replacement (dilute the acrylic primer with water) will only lead to damage to the expensive material. Unfortunately, this is unwittingly facilitated by advice found on the Internet to dissolve all acrylic paints with water.

Polyurethane primers. They are also found under the name “yacht”, since due to their high resistance to moisture they are often used for processing wooden parts of boats and other water vehicles. The peculiarity of polyurethane resins containing isocyanates requires the use of special types of thinners. The best solution would be to purchase specialized brands of thinner for polyurethane varnishes and paints, depending on the brand of primer being mixed.

Epoxy primers. They dissolve well in mixed formulations containing aromatic hydrocarbons and acetates.

Attention! When priming highly porous surfaces, the concentrate is most often not diluted. It is used thick to form a blocking crust inside the base, preventing paint from freely penetrating deep into the base. Otherwise, material consumption may increase tens of times until the entire thickness of the surface is saturated with paint.

FAQ

What is primer and undercoat thinner and what are they used for?

A thinner is a chemical preparation based on solvents that are part of the primer used. Thinners should not enter into chemical reactions with the substances that make up the primer, and also should not become the reason for delayed drying, so thinners are generally more volatile substances than solvents.

Backer thinners are used to reduce the viscosity of the liquid primer. Increased flow may be required due to the chosen method of application of the primer. For example, working with a roller instead of a brush requires a more fluid state, and when treating the surface of a yacht with a spray gun, the viscosity level must be comparable to ordinary water, otherwise the primer will clog the holes of the pneumatic sprayer.

How to properly mix thinner with primer or undercoat?

The main indicator that you should focus on when diluting the primer is the working viscosity. In professional conditions, its value is accurately measured using a special device - a viscometer. It is a measuring funnel with a calibrated hole into which paint (primer) is poured, the viscosity of which is to be measured. The hole is then opened and the flow rate of material is measured in seconds. The result is checked against table values, individual for each type of material (indicated in the quality certificate and on the label). At home, it is enough to visually assess the viscosity so that the application of the primer corresponds to the tool that is used for this.

Can the same thinner be used for different types of primers and undercoats?

It can be used only if the type of thinner is compatible in composition with the primer top. But if you want to definitely avoid problems during and after painting work, we recommend, if possible, using primers and paints and varnishes of the same line from the same manufacturer.

Can primer thinner be used in cold weather or high humidity?

Conditions for diluting primers must be specified in the instructions. These requirements must be strictly followed to ensure the quality of the backing layer and compliance with its curing/drying times. But in any case, a damp and cold surface on which the primer will be applied prevents its normal drying. Surface moisture can also impair the flow of the prepared primer.

Is there a difference in the choice of thinner for water-based and oil-based primers and undercoats?

When choosing a thinner for primers, it is necessary, first of all, to focus on the type of base layer. Depending on its base, the type of thinner is selected. Oil primers are no exception. Unlike water-based (water-acrylic) primers, oil-based ones cannot be diluted with water. To change the viscosity of oil primers, thinners based on toluene, orthoxylene, ethylbenzene, white spirit and other petroleum solvents are used.